The present invention relates to an irradiation image information read-out system, and more particularly to an irradiation image erase unit for use with a stimulable phosphor sheet in such an irradiation image information read-out system having a read-out unit, wherein the irradiation image erase unit disposed near the read-out unit is a unitary structure, simple and small in overall construction, and arranged to prevent erasure light from leaking toward the read-out unit.
There has in recent years been proposed an irradiation image recording and reproducing system in which an irradiation image of an object can be produced by using a stimulable phosphor. The stimulable phosphor, when exposed to an irradiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays, or ultraviolet rays, stores a part of the energy of the irradiation. When the stimulable phosphor exposed to the radiation is exposed to stimulating rays such as visible light, the stimulable phosphor emits light in proportion to the stored energy of the radiation. The irradiation image recording and reproducing system employs such a stimulable phosphor. More specifically, the irradiation image of an object such as a human body is stored in a sheet having a stimulable phosphor (hereinafter referred to as a "stimulable phosphor sheet" or a "phosphor sheet"), and then the stimulable phosphor sheet is scanned with stimulating rays such as a laser beam to cause the stimulable phosphor sheet to emit light representative of the irradiation image. The emitted light is photoelectrically detected and converted to an electric image signal which is processed to reproduce a visible image on a recording medium such as a photographic light-sensitive material or on a display unit such as a cathode ray tube (CRT). The aforesaid irradiation image information recording and reproducing system is disclosed in Japanese Laid-Open Patent Publication. No. 55-12429 or 56-11395, for example.
The irradiation image recording and reproducing system of the type described above is of greater practical advantage than conventional radiographic systems using a combination of an intensifying screen and an X-ray film in that images can be recorded in a wide range of radiation exposure. More specifically, it is known that the amount of light emitted from a stimulable phosphor upon stimulation thereof is proportional in a highly wide range to the amount of irradiation to which the stimulable phosphor has been exposed. Therefore, even if the amount of radiation t which the stimulable phosphor is exposed varies widely under various conditions, irradiation images free from such exposure variations can be obtained by selecting a suitable read-out gain in the photoelectric transducer for reading and converting the emitted light into an electric signal, and processing the electric signal into a visible image on a recording medium such as photographic light-sensitive material or on a display unit such as a CRT.
The irradiation image recording and reproducing system is capable of processing a converted electric signal to produce a visible image on a recording medium or a display unit so that the irradiation image can well be observed for diagnostic purpose. In this system, the stimulable phosphor sheet does not serve as a final image recording medium, but as a temporary image storage medium for eventually transferring images to the final recording medium or display unit. Therefore, the stimulable phosphor sheet can be used repeatedly, and is economical and convenient if in repetitive use.
To reuse the stimulable phosphor sheet, the residual irradiation energy on the stimulable phosphor sheet after the irradiation image has been read out by stimulating rays is discharged by exposure to light having a wavelength within the stimulating wavelength for the stimulable phosphor constituting the stimulable phosphor sheet, and the stimulable phosphor sheet is ready again for recording an irradiation image thereon. The erasure of the irradiation energy from the stimulable phosphor sheet is disclosed in U.S. Pat. No. 4,400,619, Japanese Laid-Open Patent Publication No. 56-11392 or 56-12599, for example.
An irradiation image read-out system designed to meet the above requirement includes an image read-out unit for reading out an image which has been stored in a reusable stimulable phosphor sheet by exposing it to an irradiation passing through an object, and an image erasure unit for discharging residual irradiation energy from the stimulable phosphor sheet after the image has been read out so as to allow the stimulable phosphor sheet to be reused for recording a next irradiation image. With the image read-out unit and the image erasure unit combined into one system, the system is compact in size and can be installed in a small space, and hence it is quite practical and convenient in use.
In such an irradiation image read-out system, the image read-out unit and the image erasure unit should preferably be disposed as closely to each other as possible for making system compact. However, if the image read-out unit and the image erasure unit were positioned so closely to each other that there would be no space therebetween, then certain problems would arise. When the stored image is to be read out, the stimulable phosphor sheet is exposed to stimulating rays to cause it to emit light in the pattern of the stored image, and the interior of the image read-out unit should be kept as dark as possible. The image erasure unit houses therein a light source which is as intensive as possible for discharging all of the remaining irradiation energy stored in the stimulable phosphor sheet. If any light from the image erasure unit leaked into the image read-out unit positioned closely to the image erasure unit, then the image could not be read out accurately by the image read-out unit, and no accurate irradiation image could not be obtained.